Cross guide directional couplers



Dec. 27, 1960 G. J. WHEELELR 2,966,638

CROSS GUIDE DIRECTIONAL COUPLERS Filed Dec. 15, 1954 //v l/EN T0 6 ERS'HON J. WHEEL EA ATTO/PIVE V United States Patent CROSS GUIDE DIRECTIONAL COUPLERS Gershon J. Wheeler, Newton Center, Mass., assignor to Raytheon Company, a corporation of Delaware Filed Dec. 15, 1954, Ser. No. 475,428

16 Claims. (G1. 333-) The invention relates to directional coupler structures, and more particularly, to directional couplers having improved directivity.

It is to be understood that the term directional coupler shall mean a device consisting of a first or main electromagnetic wave transmission line and a second auxiliary electromagnetic wave transmission line, each line having two ends, or terminals, the lines being coupled together at a point, or points, intermediate the ends of each, which, when there exist waves traveling in both directions in the main line, delivers to one end of the auxiliary line a voltage which is largely a function of the amplitude of the wave going in one preferred direction in the main line, and relatively independent of the wave going in the opposite direction in the main line.

It is well known in the art that if two signal channels, for example, wave guides, are suitably coupled together, for example, by being placed at right angles to each other with crossed slots appropriately positioned in their adjacent walls, a sample of energy which is being propagated in one direction in one of the guides will be fed through the aforementioned slots and be propagated in the other guide in substantially one direction only. The directivity of the directional coupler is a measure of the power that is propagated in the substantially one direction to the power propagated in the opposite direction. This invention discloses a structure whereby the directivity of any directional coupler may be increased.

Briefly, this invention comprises a first wave guide and a second wave guide, positioned substantially at right angles thereto. The coupling between said first and second wave guides may be of the single hole type, the two hole type, slots, crossed slots or any other means for coupling energy from one wave guide to another which will be apparent to a person skilled in the art.

This invention discloses a method for increasing the directivity of any directional coupler by means of a coupling hole or a plurality of coupling holes between said first and second wave guides. It has been observed from directional couplers actually constructed, that the addition of a third smaller hole in a two-hole coupler increases the directivity of the coupler.

This new eflect has been observed to increase the directivity in all the aforementioned couplers. In any coupier, cancellation inthe unwanted direction is not complete, and it is believed that the addition of a third smaller hole passes a small amount of energy which is sufficient to oppose the already small amount of energy in the unwanted direction. The addition of a plurality of holes further improves the directivity of the coupler. It is well known to persons skilled in the art that directional couplers utilizing the two-hole coupling efiect have the two coupling holes placed a quarter wave length apart, as measured along the length of the wave guide. In the directional couplers constructed in accordance with this invention, a two-hole coupler was constructed wherein the center line of said two holes was placed on a diagonal and the distance between said center line as 2,966,638 Patented Dec. 27, 1960 measured along the wave guide was a quarter wave length apart. It has been noted that placing a third hole of approximately two-thirds the diameter of either coupling hole and placed at a point where two center lines from each of the coupling holes would intersect, forming a right angle, has produced marked increase in the directivity of the coupler. Experimentation has confirmed the fact that the addition of a third hole for any directional coupler will improve the directivity of said coupler by an amount depending on the location and size of said third hole.

An object of this invention is to provide a means for improving the directivity of a directional coupler.

Further objects and advantages of this invention will be apparent as the description progresses, reference being made to the accompanying drawings, wherein:

Fig. 1 is an isometric view of a two-hole directional coupler utilizing an embodiment of this invention;

Fig. 2 is a crossed slot directional coupler utilizing an embodiment of this invention; and

Fig. 3 is a crossed slot directional coupler utilizing another embodiment of this invention.

Referring now to Fig. 1, there is shown wave guide 10 and wave guide 11 placed at an angle of approximately ninety degrees to each other and coupled to each other by means of coupling holes 12 and 13. The distance be tween the center lines of coupling holes 12 and 13 is approximately a quarter of a wave length as measured along wave guide 10. In such a structure, a wave traveling in wave guide 10 from a point called P and out at a point called P will induce in wave guide 11 a wave that travels in the direction identified as P The opposite end of wave guide 11, identified as P,,, theoretically will have zero energy for a perfect directional coupler. The action just described is the basis for all directional couplers, and the measure of directivity of such a structure is the ratio of the power at P to the power at P The amount of power actually arriving at P is that amount of energy not cancelled out by the interaction of energy arriving from holes 12 and 13. The addition of a third hole 14 has the effect of coupling energy that is out-of-phase with the resulting energy arriving at P thereby cancelling out some portion of that energy arriving at P It will be observed, therefore, that decreasing the energy at R, will increase the measure of directivity of the coupling structure.

A very susbtantial increase in coupling has been achieved by placing a third hole 14 at a point where a center line from hole 12 and a center line from hole 13 will intersect, forming a right angle. It has also been noted that the diameter of hole 14, if made approximately two-thirds the size of either hole 12 or 13, will result in a marked increase in the directivity of the coupler. It should be noted that the placement and size of the added hole is a relative matter depending on the improved directivity wanted. The information given herein should be used as an empirical guide only. For ease of construction, holes 12, 13, and 14 are drilled into wall 15 of wave guide 10. A section of wall 16 equal to the width of wall 15 of wave guide 11 is cut out, thereby allowing all the coupling holes to be made on wall 15 only. Wave guide 11 is then placed over wave guide 15 and soldered in place by a suitable silver solder, thereby fixed 1y connecting wave guide 10 and wave guide 11.

Referring now to Fig. 2, there is shown a wave guide 17 and a wave guide 18 coupled together by means of two crossed slots 19 and 20. The addition of a small hole 21 has been observed to increase the directivity, even of this efiicient directional coupler. The actual construction of slots 19 and 20 and the interconnection of wave guides 17 and 18 can be accomplished by any person skilled in the art.

- aoeaess V Referring now to Fig. 3, there is shown wave guides 22 and 23 in a directional coupler utilizing crossed slots 24 and 25 in another embodiment of this invention. There is shown in Fig. 3 a plurality of added coupling holes 26 and 27 added in accordance with this invention for the purpose of increasing directivity of the coupler. It will be noted that added holes 26 and 27 need not be of the same size as long as they are small in diameter as compared with the frequency of the propagating energy. It will also be noted that added holes 26 and 27 need not be placed on a line or in any special relationship to each other. Fig. 3 merely shows another embodiment of this invention that has been proven by empirical methods to increase directivity.

This completes the description of the embodiments of the invention illustrated herein. However, many modifications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. This invention discloses a method of increasing directivity by the addition of a hole or a plurality of holes. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein, except as defined by the appended claims.

What is claimed is:

p 1. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arrangement at right angles to said first section, said sections coupled together by a directional coupler having at least two holes, and a plurality of coupling means in addition to the holes of said directional coupler for increasing the directivity of said directional coupler, at least one of said coupling means located at the point where a line joining the center of two of said holes intersect to form a right angle.

2. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a directional coupler having first and second holes, and a plurality of coupling holes in addition to the first and second holes in said directional coupler for increasing the directivity of said directional coupler, at least one of said coupling holes located at the point where a line joining the center of said first and second holes intersects to form a right angle.

3. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a two hole directional coupler, and a single coupling hole in addition to the two hole directional coupler for increasing the directivity of said two hole directional coupler, said single coupling hole located at the point where a line joining the center of each hole of said directional coupler and that of said single coupling hole intersect to form a right angle.

4. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a twohole directional coupler, and a single coupling hole having a size of approximately two-thirds the diameter of either coupling hole of said two-hole directional coupler, said single added coupling hole placed at a point where the center lines of said two-hole coupler intersect to form a right angle, for increasing the directivity of said two-hole directional coupler.

5. In combination, a first single channel in a first section of Wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a two-crossed-slot directional coupler, and a plurality of coupling holes in addition to the two-crossed-slot directional coupler for increasing the directivity of said twocrossed-slot directional coupler, at least one of said coupling holes located at the point where a line joining the center of each of said crossed slots and that of said coupling hole intersect to form a right angle.

6. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a two-crossed-slot directional coupler, and the addition of two coupling holes in addition to said two-crossed-slot directional coupler for increasing the directivity of said two-crossed-slot directional coupler, at least one of said coupling holes located at the point where a line joining the center of each of said crossed slots and that of said coupling hole intersect to forrna right angle.

7. In combination, a first signal channel in a first section of wave guide and a second signal channel in a second section of wave guide arranged at right angles to said first section, said sections coupled together by a two-crossed-slot directional coupler, and the addition of two added coupling holes of different sizes in addition to said two-crossed-slot directional coupler for increasing the directivity of said crossed-slot-directional coupler, at least one of said coupling holes located at the point where a line joining the center of each of said crossed slots and that of said coupling hole intersect to form a right angle.

8. In combination, a directional coupler comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section; of rectangular waveguide arranged at right angles to said first section, said sections coupled together by apair of coupling holes having a center line located on a diagonal along a common broad wall, and a third hole located in said common broad wall in addition to said coupling holes for increasing the directivity of said directional coupler, said third hole located at the point where a line joining the center of each of said pair of holes and that of the third hole intersect to form a right angle.

9. In combination, a directional coupler comprising a first signal channel in a first section of waveguide and a second signal channel in a second section of waveguide arranged at right angles to said first section, said sections coupled together by a pair of coupling holes in a common broadwall of said wave guide sections, one of said coupling holes fixedly positioned at a distance of a quarter-wavelength from the other of said coupling holes as measured along the axis of said first section of waveguide, and at least a third hole located in said common broad wall in addition to said coupling holes for increasing the directivity of said directional coupler.

10. In combination, a directional coupler comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together by a pair of coupling apertures in diagonally opposite quadrants of a common broad wall section as defined by the center lines of said waveguide sections, and at least a third aperture of smaller size than said coupling apertures located in said common broad wall in addition to said coupling apertures for increasing the directivity of said directional coupler, said third aperture located at the point where a line joining the center of each of said pair of coupling apertures and that of the third aperture intersect to form a right angle.

11. In combination, a directional coupler comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together by first and second coupling apertures in a common broad wall, and a single aperture located in said common broad wall in addition to said coupling apertures for increasing the directivity of said directional coupler, said single aperture located at the point where a line joining the center of each of said coupling apertures and that of the single aperture intersect to form a right angle.

12. In combination, a directional coupler adapted to convey electromagnetic wave energy comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together by first and second coupling apertures in a common broad wall section, and a third aperture located in said common broad wall section in addition to said coupling apertures for increasing the directivity of said directional coupler, said third hole located at a point where a line joining the center of each of said first and second coupling apertures and that of the third aperture intersect to form a right angle.

13. In combination, a directional coupler adapted to convey electromagnetic wave energy comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together by a pair of coupling apertures in a common broad wall, and a third coupling aperture located in said common wall having a size of approximately two-thirds the size of said pair of coupling apertures for increasing the directivity of said directional coupler, said third aperture located at a point where a line joining the center of each of said pairs of coupling apertures intersect to form a right angle.

14. In combination, a directional coupler adapted to convey electromagnetic wave energy comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together by means of a pair of two crossed slots in diagonally opposite quadrants of a common broad wall section as defined by the center lines of said waveguides, and at least a hole located in said common broad wall in addition to said crossed slots for increasing the directivity of said directional coupler, said hole located at the point where a line joining the center of each of said crossed slots and that of said hole intersect to form a right angle.

15. In combination, a directional coupler adapted to convey electromagnetic wave energy comprising a first signal channel in a first section of Waveguide and a second signal channel in a second section of waveguide arranged at right angles to said first section, said sections coupled together by at least two crossed slots in a common broad wall of said waveguide sections, and at least a hole located in said common broad wall in addition to said crossed slots for increasing the directivity of said directional coupler said hole located at the point where a line joining the center of each of said crossed slots and that of said hole intersect to form a right angle.

16. In combination, a directional coupler comprising a first signal channel in a first section of rectangular waveguide and a second signal channel in a second section of rectangular waveguide arranged at right angles to said first section, said sections coupled together along a common broad wall by at least two crossed slots arranged in diagonally opposite quadrants of said common broad Wall, and a hole having a size smaller than the size of either crossed slots, said hole placed at the point where a line joining the center of said crossed slots and the center of the smaller hole intersect to form a right angle thereby increasing the directivity of said di rectional coupler.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,859 Moreno July 8, 1952 2,779,001 Records Jan. 22, 1957 2,870,419 Riblet Jan. 20, 1959 FOREIGN PATENTS 592,224 Great Britain Sept. 11, 1947 712,631 Great Britain July 28, 1954 OTHER REFERENCES Surdin: Directive Couplers in Wave Guides, The Journal of the Institution of Electrical Engineers, vol. 93, pt. IIIA, No. 4, 1946, pages 725-736. 

